This invention relates generally to electronic test equipment, and more particularly to test equipment including a waveform generator that converts digital signals to analog pulses representing actual physical waveforms through the use of mathematical modeling of a physical system.
Conventional arbitrary waveform generators such as the ones manufactured by Tektronix, Hewlett Packard, LeCroy, and others are used to output analog signals from a digital sequence. One application for arbitrary waveform generators is in the magnetic storage industry where devices include electronics operating at extremely high data rates. Engineers in the magnetic storage industry use arbitrary waveform generators to help with the design of the channel electronics (circuitry used to translate the analog signals output from the magnetic disks and read heads into digital signals). Arbitrary waveform generators made by Tektronix dominate the magnetic storage industry since they have the fastest rated signal speeds available today. The fastest speed available today in is one billion samples per second (1 Gs/s).
In disk drive systems, a transducing, or read/write, head writes incoming digital data onto a magnetic storage medium (the disks or platters). The incoming digital data serve to modulate the current in a coil of the read/write head so that a sequence of corresponding magnetic flux transitions are written as user data onto the magnetic medium in concentric tracks. The user data is typically divided into fixed lengths and stored in sectors of that length. Each sector of user data is stored with header information associated with it. In addition, servo information is also recorded on the disks to allow the drive to position the heads correctly over the data sectors. To read this recorded data (user data as well as headers and servo information), the read/write head passes over the magnetic medium and converts the magnetic transitions into pulses in an analog signal. These analog pulses are then decoded by the read channel circuitry to reproduce the digital data.
A disk drive is typically composed of a Head/Disk Assembly (HDA), and a Printed Circuit Board (PCB). The HDA includes an enclosed structure that contains the head and disk stacks, a disk drive motor, an actuator, and a pre-amplifier. The analog signals from the heads exit the HDA assembly and are sent through the PCB.
The PCB includes read channel circuitry on a chip that decodes the analog signals from the HDA into digital data. In order to do this, additional auxiliary signal lines (markers or gates) are also generated to keep track of whether header, servo or data fields are being read. The decoding of data has to be done very accurately in order to reproduce correctly the original digital data that was stored on the magnetic disks. The accuracy of disk drive systems is measured in error rates. An error rate of 1xc3x9710xe2x88x9210, for example, would mean only one bit was decoded incorrectly for every 1xc3x971010 (ten billion) bits processed. Although the details described above are those embodied in a magnetic disk storage system, they are also applicable to other magnetic recording systems such as magnetic tape recording systems, communication systems, and to other systems that have a physical basis onto which data is stored.
One limitation in development and testing of the channel circuitry design is that the designer has to develop the channel circuitry before the actual drive PCB (printed circuit board) and HDA (head/disk assembly) are available, due to time-to-market constraints. Another limitation is that the channel electronics are typically manufactured by a different company than the one manufacturing the disk drive system. Since the heads and disks are not available during the initial phases of the drive channel design, the engineers in both the drive company and the chip company that manufactures the channel chip use an arbitrary waveform generator and a noise source to produce an analog signal that is meant to represent the signal from the drive.
First, the engineer creates various sequences of digital bit streams that would be typically found in the final manufactured disk drive, with the assistance of a computer. These sequences are intended to represent all the aspects of signals from the disks/heads, including but not limited to the headers and data fields associated with each sector, the servo fields that allow the drive to position the head accurately within the disk surface, as well as the various tracks in the drive which typically operate at different areal densities (bit density x track density).
Once the digital bit sequence is constructed, linear superposition of an analytical function such as a Lorenzian function is typically used to create a series of ASCII characters corresponding to voltage levels to represent the analog waveform. This series of ASCII characters is stored in a data file in the computer.
The data file is provided as an input to an arbitrary waveform generator (typically manufactured by Tektronix) through a General Purpose Interface Bus (GPIB), such as an EEE 488 standard parallel interface, or any other suitable interface. Here, the ASCII characters from the data file are converted to a corresponding analog waveform.
The analog signal output of the arbitrary waveform generator is summed with the signal from a random noise generator generating xe2x80x9cwhite noise,xe2x80x9d which is random noise evenly distributed (constant amplitude) across the applicable frequency range. A white noise generator from NoiseCom is the one typically used. This final analog signal, the combination of the noise and the analog waveform is used by the engineer to study and improve the design of the read channel chip. Since the PCB which houses the read channel chip in the final disk drive system is typically not available during the design phase, the engineer uses a test fixture to house the read channel chip being designed.
At some later date in the disk drive development phase, when initial prototype HDAs are available, the analog signal from the prototype HDAs are used as a better representation. However, this usually does not represent the true distribution of signals from HDAs in production. This is because early samples of heads and disks used to make the initial HDAs are often from hand picked prototype parts from the suppliers rather than from all suppliers and manufacturing sites.
There are several shortcomings to this currently-used method of channel design. First, due to the cumbersome nature of sequence generation and input into the arbitrary waveform generator, the number of sequences of pulses that can be studied in a timely fashion are limited. Further, due to the limited amount of memory, full tracks are not easily studied since that would involve too long a sequence. Typically a single data input file, representing less than a full track length, is used through a GPIB interface to the arbitrary waveform generator.
Second, the analog pulse shape characteristics do not represent true pulse shapes of the heads and disks used in today""s disk drive systems. Features that are unique to the magnetic storage system significantly affect channel error rates. Specifically, the error rates at today""s and at future densities are significantly affected by the non-linear distortion associated with the write process and the distortions due to the magnetoresistive read head, that are commonly used today. None of these are taken into account when an analytical function is used to represent the analog signal output from the waveform generator.
Third, the channel design cannot be optimized for the final distribution of analog signals since, at best, a few hand-picked early head/disk combinations can be studied from the early HDAs built.
Fourth, the white noise that is used is of uniform amplitude at all frequencies. In reality, the actual noise in a disk drive system is not evenly-distributed white noise, but is instead colored noise. This means that the amplitude of the noise is correlated to or a function of the frequency. Using white noise does not allow accurate prediction of error rates since error rates at a given frequency are significantly affected by the signal-to-noise ratio and the actual noise is not accurately represented by white noise. However, no colored noise source is currently available to the engineer to represent the actual frequency distribution of the noise spectrum.
Fifth, disk noise, which depends on the physical nature of the disk, is unique to magnetic storage systems and has become the primary source of noise in such systems. This makes it one of the key determinants of error rates. It is not represented by either white noise or colored noise as described above and is a function of the actual physical disk. This disk noise is thus not well represented by white noise.
Finally, thermal asperities or irregularities are a phenomenon affecting the output signal waveforms in today""s disk drive systems. This phenomenon is found when using magnetoresistive read heads in close physical proximity to the diskxe2x80x94and is not represented by any of the noise sources described above.
What is needed is a system that addresses these issues in an easy to use, fast configuration that allows the study of large numbers of long sequences and distribution analysis of analog signals. Automatic generation of auxiliary signal lines (markers) that are used by the read channel would also be helpful.
The present invention relates to a device for a user to employ in developing and testing disk drive channel electronics. The device includes: a processor for controlling the device, the processor including a mathematical model of a disk drive system; a user interface for the user to communicate with the device, the user interface passing data between the user and the processor; a signal generator receiving input signals from the processor relating to the mathematical model and supplying an output signal; a noise generator supplying a noise signal in response to input signals from the processor relating to the mathematical model; and a summer that sums together the output signal from the signal generator and the noise generator. The device outputs an analog signal therefrom for application to the disk drive channel electronics.
The signal generator may include two separate signal generators supplying output signals of substantially the same frequency, and the output signals may be interleaved together to create a signal at twice the frequency of the output signals. Output signals from the two signal generators may be digital. Analog output signals may be created within a first frequency range and analog output signals may be created at frequencies lower than the first frequency range by repeating portions of the digital output signals. The portions of the digital output signals may be repeated by storing the output signals in memory in a repetitive fashion. The portions of the digital output signals may be repeated by a counter that repeats the signal a given number of times based on an input signal to the counter.
The noise signal from the noise source may be colored. The amplitude and distribution of the coloration of the noise signal may be controlled by the processor based on the mathematical model. The noise signal may be colored by a programmable filter. The device may further include a power supply that supplies power to the disk drive channel electronics. The device may further include a thermal asperity generator that supplies a signal to the summer to represent noise generated by thermal asperities in the disk drive system. The thermal asperity generator may supply an analog signal.
The mathematical model may incorporate non-linear transition shift and disk noise phenomena. The mathematical model may provide a series of input signals to the signal generator and the processor may store certain patterns that are repeated often by the mathematical model in a look-up table.
The device may further include an oscilloscope circuit for analyzing signals and providing results to the processor. The user interface may include a video monitor and a pointing device. The user interface may include a Windows-based operating system. The entire device may be housed within a PC.
The present invention also relates to a device for a user to employ in developing and testing disk drive channel electronics. The device includes: a processor for controlling the device; a user interface for the user to communicate with the device, the user interface passing data between the user and the processor; a pair of signal generators receiving input signals from the processor and supplying digital output signals of substantially the same frequency; a digital interleaving circuit receptive of and interleaving together the two digital output signals to generate an interleaved output signal of approximately twice the frequency of the digital output signals; a noise generator supplying a noise signal in response to input signals from the processor; and a summer that sums together the interleaved output signal and the noise signal. The device outputs an analog signal therefrom for application to the disk drive channel electronics.
The present invention also relates to a device for a user to employ in developing and testing disk drive channel electronics. The device includes: a processor for controlling the device; a user interface for the user to communicate with the device, the user interface passing data between the user and the processor; a signal generator receiving input signals from the processor and supplying an output signal; a colored noise generator supplying a colored noise signal in response to input signals from the processor; and a summer that sums together the output signal from the signal generator and the colored noise signal. The device outputs an analog signal therefrom for application to the disk drive channel electronics.
The present invention also relates to a device for a user to employ in developing and testing disk drive channel electronics. The device includes: a processor for controlling the device; a user interface for the user to communicate with the device, the user interface passing data between the user and the processor; a signal generator receiving input signals from the processor and supplying an output signal, a noise generator supplying a noise signal in response to input signals from the processor; a thermal asperity generator that supplies a thermal asperity signal to represent noise generated by thermal asperities in the disk drive system; and a summer that sums together the output signal from the signal generator, the noise signal, and the thermal asperity signal. The device outputs an analog signal therefrom for application to the disk drive channel electronics.
The present invention relates to a testing device for supplying application-specific test signals for portions of a system under test, the test signals simulating the signals to be generated by the remainder of the system under test. The testing device includes: a processor for controlling the device, the processor including a mathematical model of a disk drive system; a user interface for the user to communicate with the device, the user interface passing data between the user and the processor; a signal generator receiving input signals from the processor based on the mathematical model and supplying an output signal; a noise generator supplying a noise signal in response to input signals from the processor based on the mathematical model; and a summer that sums together the output signal from the signal generator and the noise signal. The device outputs an analog signal therefrom for application to the portions of the system under test.
The present invention also relates to a device for a user to employ in developing and testing disk drive channel electronics. The device includes: a PC-based computer, the computer including: a video monitor; at least one input device, and a housing; and wherein the housing includes: a processor for controlling the device, the processor including a mathematical model of a disk drive system; a user interface for the user to communicate with the device, the user interface passing data between the user and the processor; a signal generator receiving input signals from the processor based on the mathematical model and supplying an output signal; a noise generator supplying a noise signal in response to input signals from the processor based on the mathematical model; and a summer that sums together the output signal from the signal generator and the noise signal; The device outputs an analog signal therefrom for application to the disk drive channel electronics.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed descriptions taken together with the accompanying figures.